Dispersion having an insecticidal action

ABSTRACT

Dispersion containing, in addition to water, 0.5 to 20 wt. % of hydrophobic silica, 0.01 to 10 wt. % of a gelling or viscosity-increasing additive, 0.1 to 1 wt. % of a preservative and 0 to 1 wt. % of a surface-active substance. It is prepared by a procedure in which the individual components are dispersed successively or together into the water and in this procedure the individual components are deaerated before and/or during the addition or the dispersion is deaerated during the individual dispersing steps. The dispersion can be employed as an insecticide.

INTRODUCTION AND BACKGROUND

The invention relates to a dispersion having an insecticidal action, aprocess for its preparation and its use.

DE 3835592 discloses the use of hydrophobic SiO₂ for combating, forexample, sucking insects. Such materials are applied by dusting on.

However, because of the dust nuisance (industrial hygiene) duringapplication of these materials, this procedure is finding ever lessacceptance by the user. The aqueous dispersions comprising only ahydrophobic silica and water which are also described in DE 3835592,however, do not show an adequate stability.

U.S. Pat. No. 5,830,512 describes a dispersion in which an adequatestability is achieved by addition of hydrophilic substances, such as,for example, silicas. However, the active hydrophobic component isdiluted by a hydrophilic substance as a result of this. Furthermore,only a very low stability of the dispersion of hours to a few days isachieved.

It is known from EP 1 250 048 to stabilize the dispersion of hydrophobicsilicon dioxide by gelling additives, such as xanthan gum, sodiumalginates or neutralized carboxyvinyl polymers, mixtures of theseadditives also being possible.

In interplay with the hydrophobic SiO₂ particles and incorporated air,these gelling additives moreover have the effect of a significantstructural viscosity.

A pronounced structural viscosity offers advantages in application byspraying on: During the spraying process, the viscosity of thedispersion under the shear forces acting on it is relatively low. Afterthe drops of dispersion have impinged on the surface to be covered, theviscosity rises again sharply, so that dripping/running off fromperpendicular surfaces in particular is avoided.

The essential feature according to EP 1 250 048 is that in addition tothe hydrophobic SiO₂ particles to be dispersed, large amounts of air arealso incorporated. In conventional dispersing processes, this cannot beavoided without the use of wetting surfactants and defoamers. Thus, adensity of only 0.6 g/l is stated in Example 1. Approximately 40% of thevolume is therefore air.

To achieve an adequate activity, a minimum mass must be applied to thesurfaces to be sprayed. If only approximately 60% of the volume of thespraying equipment can be made use of per spraying operation, this meansa significantly reduced efficiency of the staff performing theapplication.

The transportation and packaging costs and the disposal costs of thepackaging required are adversely higher by this proportion.

An approximately 40% larger storage area must also be taken into accountduring storage.

Furthermore, a homogeneous, bubble-free covering of surfaces to betreated cannot be achieved with a dispersion containing air.

SUMMARY OF THE INVENTION

The present invention provides a dispersion comprising, in addition towater, 0.5 to 20 wt. % of hydrophobic silica, 0.01 to 10 wt. % of agelling or viscosity-increasing additive, 0.1 to 1 wt. % of apreservative and 0 to 1 wt. % of a surface-active substance.

The water content can be 68 to 99.4 wt. %.

The specific density of the dispersion can be greater than 0.6 g/ml,preferably 0.7 to 1.02 g/ml.

A pyrogenically prepared, hydrophobized silica can be employed as thehydrophobic silica. It can have a BET surface area of 20 to 600 m²/g.

The gelling or viscosity-increasing additive can be a biopolymer, suchas, for example, xanthan gum, sodium alginate, carob bean flour, pectin,agar, carrageens, alginates and/or neutralized carboxyvinyl polymer, ormixtures of these substances.

Preservatives which are approved for foodstuffs can be employed aspreservatives. These can be sorbic acid, sodium sorbate, potassiumsorbate, calcium sorbate, benzoic acid, sodium benzoate, potassiumbenzoate, calcium benzoate, PHB ethyl ester, PHB ethyl ester sodiumsalt, PHB propyl ester, PHB propyl ester sodium salt, PHB methyl ester,PHB methyl ester sodium salt, sulfur dioxide, sodium sulfite, sodiumhydrogen sulfite, sodium disulfite, potassium disulfite, calciumdisulfite, calcium hydrogen sulfite, biphenyl, orthophenylphenol, sodiumorthophenylphenolate, thiabendazole, nisin, natamycin, formic acid,sodium formate, calcium formate, hexamethylenetetramine, dimethyldicarbonate, propionic acid, sodium propionate, calcium propionate,potassium propionate.

Compounds which are also approved are: nitrates, nitrites, carbondioxide, chlorine and chlorine dioxide.

Ionic, nonionic and anionic surfactants can be employed assurface-active substances.

The invention also provides a process for the preparation of thedispersion according to the invention, which is characterized in thatthe individual components are dispersed successively or together intothe water and in this procedure the individual components are deaeratedbefore and/or during the addition or the dispersion is deaerated duringthe individual dispersing steps.

In one embodiment of the invention, the deaeration can be carried out bymeans of application of a vacuum.

DETAILED DESCRIPTION OF INVENTION

Surprisingly, a stable and active dispersion which does not containextensive amounts of air can be achieved according to the invention.This deaerated dispersion can be achieved by dispersion of previouslydeaerated hydrophobic SiO₂. A subsequent deaeration of the dispersionsis indeed technically possible, but can be achieved only with a highoutlay because of the increased viscosity of the homogeneous aqueousphase (gelling agent as an additive). At least the greatest possibleportion of the air dispersed in can be removed by deaeration measuresbefore or during the dispersing.

In principle, any dispersing process which either renders possible priordeaeration of the powder to be dispersed and also prevents dispersing inof air during the dispersing is suitable.

One embodiment of the deaeration and dispersing is the utilization of avacuum dissolver. A procedure is possible here in which water and thegelling additive are predispersed briefly, the entire amount ofhydrophobic SiO₂ is then added to the surface of the solution, withoutstirring, the container is evacuated and only then is the dispersing inof the hydrophobic SiO₂ started.

A PSI Mix® from NETZSCH can also perform this deaeration of the powder.

In order to remove residual microbubbles, deaeration units, such as theNETZSCH DA-VS vacuum deaerator from NETZSCH, a vacuum thin film rotaryprocess, can be employed.

The dispersion according to the invention can be employed asinsecticides, for example, against Housedust mite: Dermatophagoidespteronyssinus Poultry mite: Dermanyssus gallinae Rust-red flour beetle:Tribolium castaneum Grain weevil: Sitophilus granarius Indian meal moth:Plodia interpunctella Wheat aphid: Schiazaphis graminum.

EXAMPLE 1

477.5 g completely demineralized water are initially introduced into adouble-walled dispersing container of the CDS vacuum dispersing systemwith a DISPERMAT® dissolver from VMA-GETZMANN GMBH, 7.5 g xanthan gumare added, the container is evacuated (water pump) and the componentsare dispersed/dissolved at 2,000 rpm, toothed disc of 70 mm diameter,for 15 min.

15 g AEROSIL® R 202 are then added, the container is evacuated and thesubstance is incorporated into the mixture at 800 rpm.

Since air is desorbed by this process and the bubbles formed lead to anincrease in volume, the evacuation process must be interrupted severaltimes in order to allow coalescence of the air bubbles and thus aneasier deaeration. This operation is repeated until no further increasein volume of the dispersion produced takes place in vacuo. Dispersing isthen carried out in vacuo at 3,500 rpm for 15 min.

At a concentration of 3% SiO₂ and 1.5% xanthan gum, a density ofapproximately 0.95 g/ml can be achieved with this method. Theoretically,it should be possible to achieve a density of 1.02. This difference canbe explained by the formation of some microbubbles.

Such microbubbles result from the release of desorbed air constituents,after competing adsorption has taken place, by a “fine deaeration”, forexample with the aid of a NETZSCH DA-VS vacuum deaerator the density ofapproximately 1.02 can be achieved.

EXAMPLE 2

476.5 g completely demineralized water are initially introduced into adouble-walled dispersing container of the CDS vacuum dispersing systemwith a DISPERMAT® dissolver from VMA-GETZMANN GMBH, 1 g lecithin isadded, the container is evacuated briefly (water pump) and thecomponents are dispersed/dissolved at 2,000 rpm, toothed disc of 70 mmdiameter, for 1 minute.

7.5 g xanthan gum are then added, the container is evacuated (waterpump) and the components are dispersed/dissolved at 2,000 rpm, tootheddisc of 70 mm diameter, for 15 min. 15 g AEROSIL® R 202 are then added,the container is evacuated and the substance is incorporated into themixture at 800 rpm.

Since air is desorbed by this process and the bubbles formed lead to anincrease in volume, the evacuation process must be interrupted severaltimes in order to allow coalescence of the air bubbles and thus aneasier deaeration. This operation is repeated until no further increasein volume of the dispersion produced takes place in vacuo. Dispersing isthen carried out in vacuo at 3,500 rpm for 15 min.

At a concentration of 3% SiO₂, 1.5% xanthan gum and 0.2% lecithin, adensity of approx. 1.0 g/ml can be achieved with this method.

Due to the presence of a surface-active substance, the wetting of thehydrophobic silica is improved, as a result of which easier deaerationis achieved.

Theoretically, it should be possible to achieve a density of 1.02. Thisdifference can be explained by the formation of some microbubbles. Suchmicrobubbles result from the release of desorbed air constituents, aftercompeting adsorption has taken place, by a “fine deaeration”, forexample with the aid of a NETZSCH DA-VS vacuum deaerator the density ofapproximately 1.02 can be achieved.

Conventional additives for preserving, such as sorbic acids/sorbates,benzoic acidibenzoates, propionic acid, parabens (para-hydroxybenzoicacid esters) and/or Acticide® MV (Thor), can be added to the dispersionsproduced.

EXAMPLE 3

The activity was tested in Petri dishes. In this test, filter papershaving a diameter of 8.4 cm were coated on one side, with the aid of adoctor blade, with a layer thickness of 200 μm of the substance to betested and, after drying, were placed in Petri dishes of plastic havinga diameter of 9 cm. The mites (poultry mite, Dermanyssus gallinae) wereplaced in the centre of the treated surface using a fine brush. Afterapplication of the mites, the Petri dishes were closed and the lid wasadditionally secured with Parafilm. The activity tests were evaluatedafter 24 hours.

All the tests were conducted at a relative atmospheric humidity of 40%and a temperature of 26° C. The activity on the mites was determined bycounting under a stereomicroscope. A distinction was made between deadmites, severely damaged mites (severe excitation, mostly lying on theback and unable to run) and living mites in per cent compared with thecontrols.

The activity was investigated on materials which were produced inaccordance with Example 2, dispersions for which other hydrophobicAerosil types were employed instead of Aerosil® R202 additionally beingtested.

0.1% sorbic acid, 0.1% potassium sorbate and 0.2% propionic acid wereadded as preservatives during the preparation.

A batch without the addition of AEROSIL® was used as a control sample,all the other additives, including the preservatives, being identical.AEROSIL ® Dead Damaged Mortality type mites mites Living mites Totalmites % Control 0 0 103 103 0 sample R 805 56 2 52 110 51 R 974 72 0 42114 63 R 202 113 0 0 113 100 R 812 107 3 9 119 91 R 812 S 129 0 0 129100 R 8200 121 00 0 121 100

COMPARISON EXAMPLE

477.5 g completely demineralized water are initially introduced into adouble-walled dispersing container of the CDS vacuum dispersing systemwith a DISPERMAT® dissolver from VMA-GETZMANN GMBH, 7.5 g xanthan gumare added and the components are dispersed/dissolved at 2,000 rpm,toothed disc of 70 mm diameter, for 15 min. Then 15 g AEROSIL® R 202 areadded and incorporated into the mixture at 800 rpm. After theincorporation of the AEROSIL® R 202, dispersing is then carried out at3,500 rpm for 15 min. The dispersion obtained has a density of only 0.6g/ml.

Further variations and modifications of the foregoing will be apparentto those skilled in the art and are encompassed by the claims appendedhereto.

German priority application 10 2004 021 532.4 of May 3, 2004 is reliedon and incorporated herein by reference.

1. A dispersion comprising, in addition to water, 0.5 to 20 wt. % ofhydrophobic silica, 0.01 to 10 wt. % of a gelling orviscosity-increasing additive, 0.1 to 1 wt. % of a preservative and 0 to1 wt. % of a surface-active substance.
 2. The dispersion according toclaim 1, which has a specific density of greater than 0.6 g/ml.
 3. Thedispersion according to claim 2, wherein the specific density is 0.7 to1.02 g/ml.
 4. The dispersion according to claim 1, wherein the watercontent is 68 to 99.4 wt. %.
 5. The dispersion according to claim 1,wherein said hydrophobic silica has a BET surface area of 20 to 600m²/g.
 6. The dispersion according to claim 1, wherein the gelling orviscosity-increasing additive is a member selected from the groupconsisting of xanthan gum, sodium alginate, carob bean flour, pectin,agar, carrageens, alginates and/or neutralized carboxyvinyl polymer andmixtures thereof.
 7. The dispersion according to claim 1, wherein thepreservative is a member selected from the group consisting of sorbicacid, sodium sorbate, potassium sorbate, calcium sorbate, benzoic acid,sodium benzoate, potassium benzoate, calcium benzoate, PHB ethyl ester,PHB ethyl ester sodium salt, PHB propyl ester, PHB propyl ester sodiumsalt, PHB methyl ester, PHB methyl ester sodium salt, sulfur dioxide,sodium sulfite, sodium hydrogen sulfite, sodium disulfite, potassiumdisulfite, calcium disulfite, calcium hydrogen sulfite, biphenyl,orthophenylphenol, sodium orthophenylphenolate, thiabendazole, nisin,natamycin, formic acid, sodium formate, calcium formate,hexamethylenetetramine, dimethyl dicarbonate, propionic acid, sodiumpropionate, calcium propionate, potassium propionate and mixturesthereof.
 8. Process for the preparation of the dispersion according toclaim 1, comprising dispersing individual components of hydrophobicsilica, gelling or viscosity-increasing additive, preservative andsurface active substance successively or together into the water and inthis procedure deaerating individual components before and/or during thedispersing or deaerating the dispersion during individual dispersingsteps.
 9. The process according to claim 8, wherein the dispersion has aspecific density of greater than 0.6 g/ml.
 10. The process for thepreparation of the dispersion according to claim 8, wherein deaerationis carried out by means of application of a vacuum.
 11. The processaccording to claim 10, wherein a vacuum dissolver is used and the waterand gelling additive are briefly predispersed together, the hydrophobicsilica is then added to the surface of the water without stirring, thevacuum dissolver is evacuated, and then the stirring is started todisperse the silica into the water.
 12. A process for combating insects,comprising contacting insects with a dispersion according to claim 1.13. The process according to claim 12, wherein the insects are selectedfrom the group consisting of housedust mite, poultry mite, rust-redflour beetle, grain weevil, Indian meal moth and wheat aphid.